Method for manufacturing a studded tyre

ABSTRACT

A method for manufacturing a studded tyre includes producing an unvulcanized tyre, inserting studs for the tyre into seats in a curing mould, disposing the unvulcanized tyre in the mould, closing the mould, curing the tyre, and opening the mould to extract the cured tyre. The cured tyre includes a tread band including a plurality of metal studs partially projecting from a radially outer surface of the tread band. Inserting the studs for the tyre into the seats includes disposing a stud-holding device supporting a plurality of the studs inside the mould, and expelling the studs from the stud-holding device so as to dispose the studs in the seats. A stud-holding device includes a toroidal body including a plurality of through holes and an expulsion mechanism. The through holes are capable of accepting studs and the expulsion mechanism is capable of expelling the studs in a substantially radially outward direction.

The present invention relates to a method for manufacturing a studdedtyre.

A studded tyre for a vehicle wheel is particularly suitable for drivingon icy surfaces and has a tread band containing a plurality of studspartially projecting from the radially outer surface of the said treadband. The tread band usually has a tread pattern suitable for use onsnow-covered surfaces. It consists of a plurality of longitudinal andtransverse grooves that define a corresponding plurality of blocks orribs in which the abovementioned studs are inserted and from which theypartially project: a studded tyre normally has around 200/400 studs.

In their usual form, studs basically consist of a rigid body, preferablymade of steel, comprising a cylindrical or double-conical rodpossessing, at the end that is to come into contact with the road, a tipmade of a very hard material such as a tungsten carbide-based alloy, andat the other end an enlarged base to hold the stud in the tread band.

In one method for manufacturing studded tyres, the studs are fixed inthe tread band after the tyre has been cured. More precisely this methodconsists in making holes in predetermined places in the tread band forthe seats that are to contain the actual studs. The studs are placed inthese seats in such a way that the end designed to contact the roadprojects from the said band to a predetermined distance. The optionalpresence of adhesive inside each seat and the shape of each stud, inwhich the diameter of the base is greater than the rod, work together tohold the stud in position during use.

In more recent techniques, methods have been developed in which astudded tyre is produced by fixing the studs to the tread band duringcuring. For example, document EP 1 055 509 in the present Applicant'sname shows a method for manufacturing a studded tyre comprising thefollowing steps: making a green tyre, inserting and securing the studsin specific seats in a curing mould comprising sectors, inserting thesaid green tyre in the said mould, closing the said mould, and openingthe said mould to remove the said tyre once cured. The said studs areinserted in the said seats with a certain amount of play, allowing thecured tyre to be removed from the mould when the mould is opened, sothat the studs do not interfere with the sectors of the mould and sothat their essentially perpendicular position relative to the outersurface of the tread band is not affected.

The Applicant has found that although the method indicated above resultsin a more efficient procedure for manufacturing studded tyres andproduces a product with more homogeneous characteristics and greaterreliability in use, it has some drawbacks.

Specifically, the process of inserting the studs in the curing mould isperformed manually in between one curing process and the next. Since themould has a residual temperature of at least 80-90 degrees centigrade,there are many practical problems with manual insertion, especiallybecause the operation is time-consuming and laborious (at least 10-15minutes).

Moreover, this process of manual stud insertion involves an unproductiveperiod for the mould which, in addition, steadily cools down during thisprocess, necessitating a greater consumption of energy and a longerperiod of time to complete the next cure, as compared with theconsumption and time required for a mould already at temperature.

The Applicant realized that if the process of inserting the studs isdone automatically or semi-automatically, this can lead to considerableadvantages both for worker safety and for the efficiency of theproduction method.

The Applicant has found that if, during the process of inserting thestuds into the mould, a stud-holding device is used that is capable,once placed inside the said mould, of releasing a plurality of studswithin a very short space of time into corresponding seats within themould, minimal time is required for this process, which is no longerperformed manually by the workers involved.

In a first aspect, the present invention relates to a method formanufacturing a studded tyre comprising a tread band with a radiallyouter surface containing a plurality of metal studs partially projectingfrom the said outer surface, comprising the following steps:manufacturing a green tyre; inserting the said studs into seats in acuring mould; inserting the said green tyre in the said mould; closingthe said mould; curing the said green tyre; and opening the said mouldto extract a cured tyre; the said method being characterized in that thesaid step of inserting studs into the seats of the said mould isperformed by placing a stud-holding device supporting a plurality of thesaid studs inside the said mould and expelling the said studs from thesaid stud-holding device so as to locate them in the said seats.

The method of the present invention eliminates the step of inserting thestuds manually into the open mould. The studs are inserted in a simpleand practical manner on a stud-holding device during the precedingcuring of another tyre. This achieves a further considerable reductionin time and energy consumption for the next cure, because the mould isonly very briefly inactive when the studs are being inserted into it,and consequently does not waste heat. To this is also added an obviousadvantage in terms of quality of the working environment.

In a preferred embodiment of the said method, the said studs areexpelled by actuating the said stud-holding device.

In a different, preferred embodiment of the said method, during the saidinsertion step, the said stud-holding device is placed in the said mouldin such a way that each stud present in the said stud-holding device hasa position in radial alignment with the corresponding seat provided inthe said mould.

In another preferred embodiment, actuating the said stud-holding deviceproduces an outward radial force on the said plurality of studs such asto locate them in the said seats provided in the said mould.Advantageously, in another embodiment of the present method, between twosuccessive cures carried out by the same mould, a number of studs lessthan the number of seats present on the said stud-holding device isinserted in the said stud-holding device.

In another embodiment, the said stud-holding device is located centrallyin the said mould by a centring rod inserted in a seat provided on thesaid mould.

In another embodiment of the said method, the said stud-holding deviceis actuated by turning at least one lever connected to at least oneroller brought into contact with a plurality of pusher devices, eachcorresponding to a stud.

In a preferred embodiment of the method in question, the step of openingthe mould after curing is such that the studs embedded in the tread bandof the cured tyre remain approximately perpendicular to the radiallyouter surface of the said tread band.

In a second aspect, the invention relates to a stud-holding devicesuitable for placing in a curing mould for making a studded tyre,characterized in that it comprises a toroidal body, the said bodypossessing a number of through holes capable of taking studs and anexpulsion mechanism of said studs in a substantially radial outwarddirection.

The said toroidal body preferably has dimensions roughly similar tothose of a cured tyre.

In one particular embodiment, there are fewer through holes than thereare seats in the said mould.

In a preferred embodiment, the said mechanism comprises at least onelever connected to at least one roller in such a way that a rotation ofthe said lever corresponds to a similar angular movement of the spindleof the said roller.

In another embodiment, the said through holes contain a pusher devicefor transmitting to the said stud inserted therein the thrust originatedby the said mechanism.

In another embodiment, the said pusher device comprises a pistonpossessing a cap in a radially inward position designed for contact withthe said roller, a shank connected to the said cap, and a head designedfor contact with the said stud.

Other features and advantages of the invention will become clearer inthe course of the detailed description of a preferred, but not exclusiveembodiment of a method for manufacturing a studded tyre according to thepresent invention.

This description will now be set out below with reference to theattached drawings, which are supplied purely by way of indication andare therefore not restrictive. In the drawings:

FIG. 1 is a cross section through a studded tyre produced by the presentmethod;

FIG. 2 is a cross section through a sector of a curing mould adapted foruse in the method according to the invention;

FIG. 3 is a perspective view of a first embodiment of a stud-holdingdevice used in the present method;

FIG. 4 is a vertical section through the stud-holding device illustratedin FIG. 3 and of the mould in which it is inserted (showing the mouldsectors radially advanced);

FIG. 5 is a partial perspective view of the same stud-holding device andof the mould during insertion of studs into the latter;

FIG. 6 shows a top view of a second embodiment of the abovementionedstud-holding device connected to a curing mould; and

FIG. 7 is a partial vertical section through a detail of theabovementioned stud-holding device.

Referring to FIG. 1, the number 1 is a general indication for a studdedtyre produced by the method according to the present invention.

The tyre 1, which is torus-shaped, comprises a carcass structure 2 madeup of at least one carcass ply 4, reinforced with textile or metalcords, whose ends 6 are each attached to a circumferential annular core,the latter preferably being metallic and referred to below as areinforcing bead wire 8, on the radially outer surface of which beadwire is a rubber filler 12. As is known, the area of the tyre comprisingthe bead wire 8 and the filler 12 forms the bead, whose purpose is toanchor the tyre 1 to a corresponding mounting rim, not shown.

In the present case, the tyre 1 comprises a belt structure 26 which isradially external to the carcass structure 2. The latter extends roughlyfrom one side wall of the tyre to the other and comprises at least tworadially superimposed strips 28 and 30 having reinforcing textile ormetal cords parallel with each other in each layer but lying at an anglewith those of the adjacent layer and with respect to the equatorialplane of the tyre. In addition, the belt structure 26 also includes aradially outermost strip 32 possessing reinforcing textile or metalcords lying at an angle of 0°, that is in the circumferential directionof the tyre.

The radially outer surface of the said tyre 1 consists of a tread band34 designed for the rolling contact of the tyre on the ground. It has arelief design comprising grooves 22 formed within the thickness of thesaid band to define a plurality of blocks and/or ribs 18. Thecombination of these structural elements, in various configurations,generates different tread patterns, generally optimized for thedifferent forms of use of the tyre.

A series of studs 24 are inserted, as will be explained later, in thesaid tread band 34 to prevent skidding. FIG. 1 shows some of these withonly the part projecting from the outer surface of the tread band 34visible, as well as the whole body of one of them. It can be seen that,owing to the curvature of the outer surface of the tread band, the studs24, perpendicular to the said surface, are not parallel with each otherbut lie on axes y converging radially towards the middle of the tyre.

To carry out the present method, it is preferable to use a curing mouldof the type described in the abovementioned European patent applicationEP 1 055 509 filed by the present Applicant.

More precisely, the mould used is of the centripetal type comprising twoannular side portions, referred to as cheeks (not shown), which arecoaxially opposed and move axially towards and away from each other, andsubstantially correspond to the side walls of the said tyre. Betweenthese cheeks is a central annular portion comprising a plurality ofsectors (usually varying from 4 to 10 in number) arrangedcircumferentially about the axis of the mould and able to move radiallyin both directions perpendicular to the said axis. These sectors aredesigned to operate on the tread band of the tyre on which they define aso-called tread pattern: for this purpose they are provided, on theirinside surfaces designed to come into contact with the tread band, withsurface reliefs that intersect each other in varying ways to generatelongitudinal and/or transverse grooves defining ribs and/or blocks.

As regards the cheeks, if relief portions are to be formed on the sidewalls of the tyre, e.g. to define graphical identifying symbols on thetyre itself (trade mark, tyre size or other indications), these cheeksare usually provided with corresponding cavities so as to generate thesaid relief portions.

In accordance with the present invention, the mould for a studded tyre,like that shown in FIG. 1, has a series of holes (around 200/400)preformed in the sectors of the mould. Suitable devices are fitted inthe holes to hold the studs 24 in the right positions during curing,which is when the studs are embedded in the compound of the tread 34.

FIG. 2 shows a cross section of a sector of the said centripetal mould.Reference number 200 indicates the cross section of the die, i.e. theinterchangeable portion within the sectors that moulds the relief designinto the tread band.

Reference 201 indicates the inner surface of the die 200 and reference202 its outer surface.

The die 200, which is preferably aluminium, contains a plurality ofthrough holes, each having a first portion 203 running in from the outersurface 202, with a first bore diameter (e.g. 5 mm) and a second portion204 running in from the inner surface 201, with a second bore diameter(e.g. 10 mm) greater than the first diameter.

Into the second portion 204 is placed a cylindrical magnet 205 whosediameter is approximately equal to that of the hole (e.g. 10 mm) andwhose height is between 5 mm and 10 mm, preferably 5 mm.

The magnet 205 is placed up against the surface resulting from thechange in diameter of the through hole between the first portion 203 andthe second portion 204.

A bush 206, which is preferably made of non-magnetizable stainlesssteel, is then inserted into the second portion 204.

The diameter of the bush 206 is equal to that of the said second portion204 of the through hole so that, once inserted, it is held fast insidethe second portion 204 by interference close to the said magnet 205; italso forms a seat 207, the shape of which is essentially complementaryto that of the portion of the said stud 24 which will be housed insideit during the curing process.

To carry out the method according to the invention, a special tool ordevice 300 is used to hold a number of studs 24 equal to or less thanthe number of the said seats 207 present in the mould.

More precisely, as illustrated in FIGS. 3 to 6, the said stud-holdingdevice 300 is preferably a torus shape roughly the same as that of themoulded and cured tyre.

The said stud-holding device 300 may for example be made by casting asynthetic material and then machining it with machine tools to form allthe geometrical and structural features described below.

The toroidal body of the said stud-holding device 300 advantageouslyincludes a number of through holes 301 that is equal to or less than thenumber of seats 207 present in the said mould for holding the studs 24during the curing process.

In each of the said holes 301, in a radially inward position, is apusher device, such as a spring-loaded piston 303 (FIG. 7) or anequivalent device which, as will be explained later, will push theassociated stud 24 in a radially outward direction during the insertionof the said stud 24 into the mould. More precisely, the said piston 303comprises, when assembled on the said stud-holding device 300, a cap 304in a radially inward position and preferably made of brass, the said capbeing connected to one end of a shank 305 which is preferably made ofaluminium and has a head 306 in a radially outward position designed toimpact the said stud 24. Also connected to the body of the shank 305 isa spring 307 for returning the piston 303 to the rest position after ithas performed its pushing function.

A magnet 308 is advantageously provided in a position that is radiallymore external than the said head 306 in the rest position, and axiallymore external or more internal than the said hole 301, so as to exert anattractive force on the stud 24, placed, as will be explained later,close to the said head 306, sufficient to keep it in position.

In a radially more external position, the said hole 301 also flares outto allow removal of an undercut following the said casting; thebasically cylindrical wall of the said hole 301 in the said radiallymore external portion and the said head 306 define a seat 309 in whichto house a stud 24.

The said stud-holding device 300 is surmounted axially, as illustratedin FIGS. 3 to 6, by a mechanism 310 that makes it possible to exertpressure in sequence on the radially inward ends of each piston 303.

The said mechanism 310 preferably comprises a plurality of attachmentbars 311, numbering four for example, arranged radially at angles ofapproximately 90 degrees with respect to each other. The bars arepreferably made of aluminium alloy. At their point of intersection, i.e.along the axis of the said stud-holding device 300, is a handling means,such as a hook 312, for handling the said stud-holding device.

The abovementioned attachment bars 311 support, preferably in thevicinity of the abovementioned point of intersection, a rotating beam313 carrying at its free end at least one roller 314, preferably made ofPTFE, designed to make contact with the radially inward ends of the saidpistons 303, that is with the brass caps 304 of the latter. The saidroller 314 is preferably connected to the said rotating beam 313 by abracket 315 hinged to this beam. Rotation of the said bracket 315 aboutits hinge point connecting it to the said rotating beam 313advantageously allows the roller 314 to move into or out of contact withthe said caps 304. More exactly, if the straight line joining the pointof intersection between the axis of the roller 314 and the bracket 315to the said hinge point on the bracket 315 forms an angle of 0 degreeswith the radial direction of the rotating beam 313, the roller 314 willbe in its radially outermost position and in contact with the said caps304; whereas if the said angle is other than 0 degrees, for example 45degrees., the roller 314 will be in a radially more inward position (seeFIG. 6) and not in contact with the said caps 304.

Circumferential movement of the rotating beam 313 and consequently ofthe roller 314 is provided by one or more angularly staggered coplanarlevers 316 (see FIGS. 5 and 6) which are axially further out than thefour attachment bars 311. As shown in FIGS. 4, 5 and 6, the said levers316 are connected, preferably by a shaft along the axis of thestud-holding device 300 to the said rotating beam 313, so that anyrotation by them about the said axis causes a corresponding rotationalmovement of the said rotating beam 313 about the same axis.

The stud-holding device 300 may also include a centring mechanism 320for defining its position with respect to that of the said curing mouldduring the insertion of the studs 24 into the mould.

The said centring mechanism 320 comprises, for example, a centring rod321 connected mechanically to the toroidal body of the said stud-holdingdevice 300, for example by a bracket 322, which allows it to moveradially due to the elasticity of a spring (not shown in the figures).The said rod 321 is designed to fit into a special seat 323 provided inthe mould before the studs 24 are inserted, as will be explained below.Advantageously, the position adopted by the stud-holding device 300within the mould, when the rod 321 is inserted in the seat 323, is suchthat each stud 24 placed in the said seat 309 is in radial alignmentwith the corresponding seat 207 in the die 200 of the said mould.

Studs 24 that can be used in the method according to the invention maybe, for example, those described in the abovementioned document EP 1 055509 filed by the present Applicant.

These basically have a central body consisting of a rigid component,preferably made of steel or other ferromagnetic metallic material (suchas CF17 SMnPb10, UNI 4838/90).

The said stud 24 has a cylindrical, or more preferably tapered enddesigned to project from the radially outer surface of the tread band.This end may also conveniently be fitted with a tip of hard metal, suchas tungsten carbide, inserted in the body of the stud 24 for increasedgrip on snow-covered and/or icy surfaces.

At the opposite end from the said tip, the stud 24 comprises apreferably circular base whose diameter is greater than any otherdiameter of the said central body. The part of the stud 24 lying betweenthe tip and the base may include along its axial length one or moreannular ridges approximately equal in diameter to the diameter of thebase, in order to improve the adhesion of the stud 24 within the treadband.

After being cleaned, for example by sand blasting and/or phosphating,the stud 24 is treated before use with a binding agent, preferably byimmersion, to greatly increase the adhesion between the compound of thetread band and the external surface of the stud during curing of thetyre.

The method according to the invention comprises a plurality ofsuccessive steps.

A green tyre is first manufactured. Then, after a plurality of studs 24have been inserted in the seats 207 provided in the said mould, the saidgreen tyre is inserted in the said mould. The latter is then closed andthe said tyre is moulded and cured. The mould is then opened and thecured tyre removed with the said moulded tread band 34 containing thesaid plurality of studs 24.

The studs 24 embedded in the tread band 34 of the cured tyreadvantageously do not slide against the walls of the said seats 207during removal from the mould, as they remain more or less perpendicularto the radially outer surface of the said tread band 34, thus avoidingproblems both for the mould and for the integrity of the tyre itself.This happens because each stud 24 has a predetermined amount of playwithin its own seat 207 inside the mould, sufficient to allow this studto undergo movements of its own axis relative to the axis of the seat.In other words this enables the sector of the mould to withdraw off thestud as the mould is being opened, by a movement in an inclineddirection with respect to the axis of the stud 24. The stud is thereforenot subject to bending forces, or to traction by friction with the wallof the bush 206, and as a consequence the interface of attachmentbetween the compound of the tread band 34 and the surface of the stud isnot stressed.

The step in which the said studs 24 are inserted into the said mould isperformed according to the invention in a series of substeps asindicated below.

The said stud-holding device 300 is loaded with a plurality of studs 24while preferably suspended off the ground by means of the hook 312, tofacilitate the work of the operators who insert, for example manually,the plurality of studs 24 (around 200/400) into the corresponding seats309 present in the radially outer surface of the said stud-holdingdevice 300. The magnets 308 act in conjunction with the said seats tohold the studs in position as soon as they are loaded. Depending on thetype of tyre to be produced, the number of studs 24 inserted into thesaid stud-holding device 300 by the staff is equal to or less than thenumber of seats 309 present in the device.

Next, the said stud-holding device 300 is inserted, handling it with thehook 312, inside the mould, which has just been opened, for example toremove a freshly cured tyre. The stud-holding device 300 is then securedto the mould by means of the centring rod 321 which is housed in theseat 323 provided in the said mould. In this way, as already indicated,the (radially outermost) tip of each stud 24 will be in radial alignmentwith the corresponding seat 207 in the die 200 of the said mould.

The operators then check that the roller 314 is inserted, that is to saythey adjust the angular position of the bracket 315 as explainedearlier, so that the roller 314 can contact the radially inward ends ofthe pistons 303, that is the caps 304.

With the stud-holding device 300 fixed in the centre of the mould, thesectors of the latter can be moved in with a radial movement and then,by acting on the lever or levers 316, the roller 314 is turned and, byapplying pressure to the said caps 304, the roller produces a radialmovement of the heads 306 of the pistons 303, which expel the studs 24connected to them in a radially outward direction. Simultaneously, eachmagnet 205 located in a radially outward position relative to the seat207 exerts an attractive force on the corresponding studs 24 expelledfrom the said stud-holding device 300. Each stud 24 thus ends up in thecorresponding seat 207 in the mould which, as mentioned earlier, is of acomplementary shape to that of the tip of the said stud 24, while eachmagnet 205 continues to exert its attractive force and hold thecorresponding stud 24 in position throughout the subsequent steps. Oncethe roller 314 has completed its action on each piston 303, the spring307 returns the cap 304 to position. When the roller has covered theentire radially inner surface of the device 300, that is when the levers316 have completed one 360 degree revolution (and this preferably takesplace in a few seconds), all the studs 24 will be inside the said mould.

At this point the sectors of the mould are opened again to allow thestud-holding device 300 to be withdrawn. A green tyre is then placed inthe mould, the mould is closed and the moulding and curing step begins.In the meantime the studs for the next cure are being inserted in thesaid stud-holding device 300.

At the end of curing, a studded tyre such as that explained above isremoved from the above-mentioned mould, which remains open and inactiveonly long enough for the studs 24 to be transferred from the saidstud-holding device 300, which is already ready for use.

The method described above therefore solves the problems encountered inthe prior art, avoiding both excessive down times in the use of themould and safety problems for the workers.

1-14. (canceled)
 15. A method for manufacturing a studded tyre,comprising: producing an unvulcanized tyre; inserting studs for the tyreinto seats in a curing mould; disposing the unvulcanized tyre in themould; closing the mould; curing the tyre; and opening the mould toextract the cured tyre; wherein the cured tyre comprises a tread band,wherein the tread band comprises a plurality of metal studs partiallyprojecting from a radially outer surface of the tread band, and whereininserting the studs for the tyre into the seats comprises: disposing astud-holding device supporting a plurality of the studs inside themould; and expelling the studs from the stud-holding device so as todispose the studs in the seats.
 16. The method of claim 15, whereinexpelling the studs comprises actuating the stud-holding device.
 17. Themethod of claim 15, wherein during inserting the studs into the seats,the stud-holding device is disposed in the mould so that each stud inthe stud-holding device comprises a position in radial alignment with acorresponding seat in the mould.
 18. The method of claim 16, whereinactuating the stud-holding device produces an outward radial force onthe studs to dispose the studs in the seats.
 19. The method of claim 15,wherein between two successive cures carried out in the same mould, anumber of studs are inserted into seats in the stud-holding device, andwherein the number of studs inserted in the stud-holding device is lessthan a number of seats in the stud-holding device.
 20. The method ofclaim 15, wherein the stud-holding device is disposed centrally in themould by a centering rod disposed in a seat provided in the mould. 21.The method of claim 16, wherein actuating the stud-holding devicecomprises turning at least one lever connected to at least one rollerbrought into contact with a plurality of pusher devices, and whereineach pusher device corresponding to a stud.
 22. The method of claim 15,wherein during opening the mould, the studs partially projecting fromthe tread band remain approximately perpendicular to the radially outersurface of the tread band.
 23. A stud-holding device, comprising: atoroidal body; wherein the body comprises: a plurality of through holes;and an expulsion mechanism; wherein the through holes are capable ofaccepting studs, and wherein the expulsion mechanism is capable ofexpelling the studs in a substantially radially outward direction. 24.The device of claim 23, wherein the toroidal body comprises similardimensions to those of a cured tyre.
 25. The device of claim 23, whereinthere are fewer through holes in the body than seats in a correspondingmould.
 26. The device of claim 23, wherein the expulsion mechanismcomprises at least one lever connected to at least one roller so that arotation of the at least one lever corresponds to a similar angularmovement of a spindle of the at least one roller.
 27. The device ofclaim 26, wherein the through holes comprise a pusher device fortransmitting thrust generated by the expulsion mechanism to the studs inthe through holes.
 28. The device of claim 27, wherein the pusher devicecomprises: a piston; a shank; and a head; wherein the piston comprises acap in a radially inward position, wherein the cap is designed forcontact with the at least one roller, wherein the shank is connected tothe cap, and wherein the head is designed for contact with acorresponding stud.